Picturing DNA
Chapter 5:
DNA and Race

Introduction

Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 6

Chapter 7

Epilogue

In the not-too-distant past, most people assumed that mankind could be divided into subcategories of people whose skin color, body shape or facial features were different enough to mark them as members of distinct races within the human species. Many people still make this assumption. To them, the claims of the Lemba people, a remote tribe living in the northeast corner of the Union of South Africa, are problematic. The Lemba insist that their practice of circumcision, their avoidance of eating pork and an oral history that traces their origins to the Middle East prove that they are Jews-and Jews by descent, not by conversion.

The Lemba are black. They believe that their ancestors came from the land of Israel, probably passed through southern Arabia and, centuries ago, crossed over into Africa. But they certainly don't look "Jewish," and the mainstream Jewish community has not taken their claim of kinship to heart. If they really are Jews, what does this tell us about our assumptions of racial identity?

As recently as 1962, Carleton Coon, a prominent anthropologist, published a best-selling book called The Origin of Races, which neatly divided human beings into five "races" he called Caucasoid, Mongoloid, Australoid, Negroid, and a group he called Capoid (named for the Cape of Good Hope). In this last category, Coon lumped together southern tribes, like the Bushmen and Hottentots, and some tribes from eastern Africa who had dark skin but did not otherwise fit well into his description of Negroid people. He speculated that since there were pygmies among them, perhaps they had a genetic propensity to shrink. Coon argued that these races were descendants of five different subspecies of humans that had existed in the Middle Pleistocene era and had evolved independently into races of Homo sapiens. According to Coon, the Caucasoids, who he believed had evolved first, were by implication a bit further up the ladder of civilization.

Coon, like most physical anthropologists, based his distinctions among races on observable characteristics such as skin and eye color, facial features and body shape-what contemporary biologists call the phenotype. Today, human geneticists have begun to group people according to less visible markers-the genes we carry on the chromosomes in each of our cells. Biologists call this the genotype.

Just as paleontologists now rely on carbon dating to ascertain the age of fossils and inorganic objects like the stones in Stonehenge, molecular biologists now look to the genotype to trace human heredity. Within each of their body's cells, human females carry mitochondria, tiny entities that have their own DNA. Mitochondrial DNA enables geneticists to track characteristics that are passed from mother to daughter. In contrast, all human males carry a Y chromosome, which is passed from father to son and remains remarkably stable down through generations.

Late in 1997, a group of British geneticists embarked upon a curious enterprise. They gathered DNA samples from a randomly chosen group of Jewish men enjoying themselves at a beach in Tel Aviv. Some of the men, because their surnames were variations of the name Cohen, could claim to be members of the priestly tribe of Cohanim, which by tradition traced its ancestry back to the biblical tribe of Levi. Since membership in this priesthood is transferred from father to son, researchers decided to look for distinctive patterns on the men's Y chromosomes.

A particular set of genetic markers that are extremely rare in the non-Jewish population showed up in about 10 percent of the Tel Aviv beachboys. This marker is suggestive of Jewish ancestry whenever it is found; it probably existed in the ancestral Hebrew population and was passed on through the centuries to males in contemporary Jewish communities. But most astounding was the discovery that these markers appear in over 50 percent of men who claim to be Cohanim. Thus, the markers came to be called the Cohen Modal Haplotype.

The English geneticists were on a roll. They then collected DNA samples from men of the Lemba tribe, as well as from the males in a group of Yemenites still living in the region of southern Arabia from which the Lemba traditions indicated they had lived before they migrated to southern Africa. They found sufficient genetic similarities between the Lemba and the current Yemenites to suggest that they are kinsmen.

But are they Jews?

The geneticists found that the proportion of Lemba men carrying the genetic signature of Cohanim was about 10 percent, similar to the percentage found among Jewish men around the world and much higher than found in the general population. Moreover, the Cohen Modal Haplotype appeared in about half of one particular group of Lemba-the Buba clan, the most prestigious of all Lemba clans. This is strong evidence that the Lemba are genetically connected to worldwide Jewry and that the Buba clan are not only Jewish, but belong to the hereditary priestly class.

This genetic bulletin provides validation for the Lemba and important news to the worldwide Jewish community about their far-flung cousins. But it is equally fascinating for what it tells everyone about race. This surprising genetic link between a tribe of black Africans and their European and Middle Eastern cousins suggests that if there is such a thing as race, it isn't a matter of skin color or a prominent nose.

Take a look at the Irish. Using techniques similar to those that the British geneticists had used in their search for Jewish continuity, molecular biologists at Trinity College in Dublin combined research into ancient Irish surnames with DNA analysis. They substantiated the claim that men from Connaught, a western province, were descended from a population of hunter-gatherers who migrated there 9,500 years ago from the Near East. They, in turn, are thought to have descended from a group that had occupied Europe an estimated 30,000 years ago, after the Neanderthals had left, and settled in northern Spain before some of them continued on to Ireland. The Irish may not look like their cousins the Basques, who stayed put in the area of what is today the border between Spain and France, but many of them carry the same telltale genetic marker.

The six billion human beings alive on the Earth today have very different phenotypes. That is, there are obvious differences in our skin color, hair color and texture, facial shape, facial features, body size and proportions. In the eighteenth century, Carolus Linnaeus, the Swedish scholar who created the first scientific classification of animal species, was among the first to attempt a scientific description of the subspecies, or "races," that distinguish human beings. Many variations followed. Usually these efforts identified three or four races, most commonly called Negroid or black, Caucasian or white, Mongoloid or yellow, and Amerindian or red. By the nineteenth century, the system builders linked these physical traits to sexual practices and moral character or to academic skill. Not surprisingly, these supposedly "scientific" racial attributes reflected the biases of the European or American (certainly Caucasian) males who devised the system. For example, British writers tended to label dark-skinned, narrow-featured inhabitants of the Indian subcontinent as members of the Negroid race, reflecting their colonial prejudices, whereas Americans, who had no imperial axes to grind, tended to consider such people as Caucasian.

The first challenge to the categorizing of human beings according to these theories came from the anthropologist Franz Boaz. He argued that most of the differences between people were cultural, not physical, and that whatever physical differences did exist were too muddled to make sense. Boaz's argument was substantiated by studies of human migrations, language affinities and, after the 1940s, by the study of blood-group frequencies.

Blood is a curious substance with an often-mystical role in human religious practices. Flowing blood indicates life. The natural release of blood in women of childbearing age, the ancient practice of purging blood from the sick, as well as the ritualistic drinking of blood as a Christian sacrament, place this particular bodily fluid in a special symbolic category.

We speak of someone having "Italian blood" or "Chinese blood," of "bad blood" and "good blood," but there is no such thing. With a few minor exceptions, the four blood groups-A, B, AB and O-are found in all human populations. The A blood of a Norwegian is compatible with the A blood of a Zimbabwean, as the type O blood of a Vietnamese can be successfully transfused into a Peruvian. There are, as in most things human, a few fascinating anomalies: a large percentage of Germans have the same distribution of blood types as do a large number of New Guineans, and similarly, a high percentage of Estonians show nearly the same distribution as a high percentage of Japanese. The distribution patterns of the human blood groups tell us nothing about the alleged races of mankind.

DNA, however, is altogether different. Genetic information, such as that linking the dark-skinned Lemba to the beige-colored European Jews, effectively challenges efforts to divide humankind into any racial groups at all. Today most anthropologists, biologists and geneticists who use the word "race" understand it as verbal shorthand to describe a few visible phenotypical characteristics with no scientific meaning.

Skin color, body shape and facial features turn out to be superficial characteristics that seem to have arisen in response to local environmental conditions. The differences between members of any one so-called race are usually greater than the similarities that supposedly mark them off from members of another "racial" group.

Take skin color, the most obvious "racial" marker. Variations in skin color are based on the amount of a chemical called melanin. Many scientists believe that since melanin protects the skin from damage produced by exposure to the ultraviolet rays of the sun, those people who live in areas where they are likely to be exposed to a great deal of sunlight-close to the equator or in open deserts-are likely to have adapted to their environment by having more individuals with a lot of melanin survive to the age of reproduction and therefore have darker skin than people who live in temperate regions. Others believe that varieties of skin color have more to do with sexual selection. They believe that in some communities females were attracted to darker- or lighter-skinned males, and so chose them as mates. But however the localized variations in skin color evolved, there are no rigidly definable categories. People come in colors that range from the very darkest among populations that are generally dark-skinned to the very lightest among light-skinned people and cannot be divided into separate "races."

This does not mean that we cannot speak of people as members of distinct ethnic groups or diverse human populations. Individuals inherit their genes from their parents, who inherited them from their parents, and so on back through time. To the degree that our ancestors lived in one area of the world for many generations and therefore chose their mates from within a finite pool of people, some specifics of a genetic heritage will have emerged. The genome of Australian aborigines, for example, will differ ever so slightly from that of the Inuit people who have lived in the Arctic.

DNA analysis has recently opened a door to new information about the very origins of the human race. A team of scientists at Emory University School of Medicine, using DNA analysis of the mitochondrial material carried only in egg cells and therefore through the lines of female descent, and a similar group working with DNA analysis of the Y-chromosome male line, have both traced the genetic history of our species back to one common ancestor of each sex who lived in central Africa approximately 150,000 years ago. Their work implies that everyone living today is descended from these two people. Of course, this genetic Adam and Eve were not the only humans alive in their day, but evidence suggests that all of the descendants of their peers died out centuries, even millennia, ago.

The same DNA patterns that point to our being just one big happy family also reveal just when and how it was that some of our clan first moved away from home. Tiny variations in DNA among people from different parts of the world indicate that some folks left Africa and settled in Asia between fifty-three thousand and seventy-three thousand years ago; others moved toward Europe some forty thousand to fifty thousand years ago; and some of the population that had settled in Asia and Europe moved on the Americas seven thousand to thirty-five thousand years ago. The Asians traveled across the Bering Sea; the route the Europeans took is unknown.

Within the populations living on a specific continent, geneticists have identified a number of subgroups, some twenty-eight in all, that enable them to trace the moments of people as they spread out, colonizing different regions and then settling down to form distinct communities. Scholars have suggested that there are correlations between these subgroups and various language groups. For example, a linguist at Stanford University speculates that there is a parallel between three major subgroups of American Indians as evidenced by differences in their mitochondrial DNA and by the three main language groups of the Amerindian population.

These kinds of genetic patterns are already making it possible for people whose ancestral history is tantalizingly vague to fill in gaps in their family tree. A British company has announced that it will analyze the DNA of European customers who submit a sample of cells from the inside of their mouths and tell them from which of seven European subgroups they are descended. A recently established registry for African Americans offers to match samples of their DNA to that of people from different areas of western Africa in an effort to help them discover their likely ethnic roots. Similarly, adoptees or orphans who know little about their biological roots might someday be able to identify where their biological forebears most likely came from by consulting a kind of DNA-specific map of the world that would correlate genetic markers with geographical locations.

Since all people on Earth are descended from the same ancestors, our genetic variations can be looked at as a record of the paths followed by subsequent generations. In addition to verifying the genetic histories of the Lemba tribesmen and the villagers of Connaught, DNA evidence was recently brought to bear on a question that had baffled students of Finnish culture for years. The Finns speak a language that has few connections to the Indo-European tongues spoken by their neighbors. The closest linguistic cousin of Finnish is the Magyar language spoken by Hungarians, even though the similarities are not all that close. Perhaps the Finns' language preserves a snapshot of the original population of Finland, which we know was conquered centuries ago by invaders from the steppes of central Asia. Most historians have long assumed that the invaders wiped out the local population. But others interpret the preservation of the ancient language as a sign that the conquerors and conquered intermarried. DNA evidence recently was used to settle the argument. The mitochondrial DNA in contemporary Finnish women indicates the persistence of genes from the aboriginal population. After the invaders won the war and killed off the men who opposed them, they mated with the local women, who transmitted the invaders' language and genes to the present-day Finnish population.

DNA evidence can even be used to validate personal histories based on oral traditions that heretofore have been disparaged. For nearly two hundred years, the descendants of Sally Hemings, a black slave who belonged to Thomas Jefferson, handed down family legends that Jefferson was the father of Hemings' six children. In 2000, after years of denying that the story had any merit, the Thomas Jefferson Memorial Foundation, which owns the Jefferson homestead at Monticello and speaks for many of the third president's living descendants, acknowledged the results of a 1998 test comparing the DNA of several current-day descendants of Jefferson and Hemings. The test results concluded that a Jefferson male had probably been the father of Hemings' youngest son, Eston. There is no evidence placing the only other likely candidates-the president's brother or his nephews-at Monticello during the time Hemings would have conceived Eston. Therefore, the foundation president announced, the test "suggests the strong likelihood" that Jefferson fathered one, and possibly all, of Hemings' children.

DNA evidence can be used to validate or disprove the claims of people with aspirations to royalty. Posthumous tests made it clear that a woman who had convinced millions that she was Anastasia, daughter of the last Romanov rulers of Russia, was, in fact, a German born to an ordinary family with no ties of any kind to the family of the tsars. Conversely, DNA analysis confirmed the assertion by loyalists to the Bourbon kings of France that a heart that had been preserved by happenstance was really that of the martyred 10-year-old son of Louis XIV.

Fruitful as these exercises may be for historians, keepers of the flame of royalty, and individuals and their families, the more general application of DNA analysis linked to population subgroups lies in the area of medical research. Some localized gene pools contain a high frequency of otherwise rare characteristics that have made them fascinating study areas for geneticists. A single mutation in an individual's genes some generations back probably provided some kind of adaptive advantage and therefore spread rapidly as more people with this mutation survived into adulthood and transmitted the gene to their children and grandchildren. A good example of this is the sickle-cell variation in some blood cells that confers a protection against malaria to people living in parts of sub-Saharan Africa, southeast Asia and the Mediterranean basin where malaria is common. The variation spread through local populations, and their descendants retain a disproportionate likelihood of carrying that trait even though they no longer live in malarial areas. A single gene for the sickle-cell trait still protects against malaria. But should someone inherit the sickle cell from both parents, the result is a condition known as sickle-cell anemia, which is painful and life-limiting. Similarly, Tay-Sachs disease is caused by a genetic anomaly that is thought to confer some protection against tuberculosis and is unusually prevalent among people of eastern European descent, particularly Jews, who may have lived in squalid conditions where tuberculosis thrived. A double dose of the Tay-Sachs gene results in a condition that stops a child's development around the age of two and is usually fatal before the child's fifth birthday.

Sometimes a community's genetic history is well enough known that the source of a distinguishing condition can be traced to a single individual. This so-called founder's effect explains the high incidence of conditions like porphyria (symptoms include extreme sensitivity to light) among white South Africans and Huntington's disease among the inhabitants of several isolated Venezuelan villages.

Disease clusters fascinate students of genetic transmission in large part because they can be traced to mutations in one gene. But most inherited tendencies- from cancers to talents in academic achievement, athletics, art or music-result from the interplay among many genes and the effect of the individual's environment on those genes.

Today, many anthropologists speak of clines, or gradations, to distinguish between degrees of genetic closeness that include differences in skin color, propensity toward diseases, and all the other factors-visible and hidden-that make us what we are. Geneticists speak of lineages, or haplotypes, when they describe the different subgroups that have descended from our common ancestors. The old distinctions between what were once called races persist in everyday speech, but they are becoming linguistically and ideologically obsolete and as far removed from science as the once exalted study of alchemy.

Return to Table of Contents Return to Previous Chapter Go to Next Chapter

To see an interview with Dui Seid, click here

Picturing DNA by Bettyann Holtzmann Kevles & Marilyn Nissenson
Copyright © 2000 Bettyann Holtzmann Kevles & Marilyn Nissenson
All Rights Reserved